A bit sloppy implimentation of Google Maps, MarkerClusters.js, and Wordpress location custom fields.

mapmarkerwordpress.php

<?php
//Grabbing locations depending on the page
if ( is_page( 'facilities' ) ) {
	$metaValue = 'facility';
} elseif ( is_page( 'dropoff' ) ) {
	$metaValue = "dropoff";
} else {
	$metaValue = "event";
}


$args = array(
	'post_type' => 'location',
	'meta_key'  => '_location_type',
	'meta_value' => $metaValue
);

$location_query = new WP_Query( $args );

$location_array = array();
if ( $location_query->have_posts() ) : while ( $location_query->have_posts() ) : $location_query->the_post();

	$loc_lat  = get_post_meta( $location_query->post->ID, '_location_lat' );
	$loc_name = get_post_meta( $location_query->post->ID, '_location_name' );
	$loc_lng  = get_post_meta( $location_query->post->ID, '_location_lng' );
	$loc_addr = get_post_meta( $location_query->post->ID, '_location_address' );
	$loc_type = get_post_meta( $location_query->post->ID, '_location_type' );
	$loc_desc = get_post_meta( $location_query->post->ID, '_description' );

	//Shove into array
	$loc_array[] = array(
		'name' => $loc_name,
		'lat' => $loc_lat,
		'lng' => $loc_lng,
		'addr' => $loc_addr,
		'type' => $loc_type,
		'desc' => $loc_desc
	);
endwhile; endif;
wp_reset_postdata();

?>

<script	src='https://maps.googleapis.com/maps/api/js?key=API_KEY&sensor=false&extension=.js'></script>

<script>
	google.maps.event.addDomListener(window, 'load', init);
	var map;
	function init() {
		var mapOptions = {
			//center: new google.maps.LatLng(39.690281,-92.695314),
			zoom: 5,
			map: map,
			zoomControl: false,
			disableDoubleClickZoom: false,
			mapTypeControl: false,
			scaleControl: false,
			scrollwheel: false,
			panControl: false,
			streetViewControl: false,
			draggable: false,
			overviewMapControl: false,
			overviewMapControlOptions: {
				opened: false,
			},
			mapTypeId: google.maps.MapTypeId.ROADMAP,
		}

		var mapElement = document.getElementById('vt-locations');
		var map = new google.maps.Map(mapElement, mapOptions);
		var image = '<?php echo get_template_directory_uri(); ?>/css/images/green-marker.png';
		var bounds = new google.maps.LatLngBounds();
		var iw = new google.maps.InfoWindow();

		var locations = <?php echo json_encode($loc_array); ?>;

		var markers = [];
		for (i = 0; i < locations.length; i++) {
			marker = new google.maps.Marker({
				icon: image,
				position: new google.maps.LatLng(locations[i].lat[0], locations[i].lng[0]),
				title: locations[i].name[0],
				address: locations[i].addr[0],
				desc: locations[i].desc[0]
			});

			//Setting bounding boxes and starting clusters
			bounds.extend(marker.position);
			markers.push(marker);

			<?php if(is_page('facilities')) { ?>
			google.maps.event.addListener(marker, 'click', function () {
				var html = "<div style='color:#000;background-color:#fff;padding:5px;width:150px;'><h4>" + this.title + "</h4><p>" + this.address + "<p><p>" + this.desc + "<p></div>";
				iw.setContent(html);
				iw.open(map, this);
			});
			<?php } ?>
		}

		//Clusters and bounds
		var clusterStyles = [
			{
				url: '<?php echo get_template_directory_uri(); ?>/css/images/green-marker.png',
				height: 32,
				width: 24,
				textColor: '#000000',
				textSize: 18
			}
		]

		var markerCluster = new MarkerClusterer(map, markers, {
			styles: clusterStyles
		});

		map.fitBounds(bounds);
	}
</script>